1. Field of the Invention
The present invention relates to supercritical fluid-based compositions and methods useful in semiconductor manufacturing for the removal of unwanted material from semiconductor manufacturing equipment as well as semiconductor substrates and device structures.
2. Description of the Related Art
In the field of semiconductor manufacturing, many different types of cleaning reagents are utilized for removing unwanted material from process chambers as well as substrates and microelectronic device structures. Examples include removal of flux employed in connection with bonding of integrated circuitry devices and packages, cleaning of chemical reservoirs for use in deposition operations, and cleaning of substrates and device structures to remove post-etch, lithographic resist residue, and removal of chemical mechanical planerization slurry particulates in deep trench, high aspect ratio structures.
Each of these semiconductor manufacturing cleaning operations is further discussed below.
In the fabrication of integrated circuit packages, and the manufacture of microelectronic components generally, fluxes frequently are employed to join electronic components by soldering processes. The function of the flux includes thermally-activated removal of surface oxide films (e.g., surface oxides of metals such as copper, nickel, gold-coated copper and gold-coated nickel) from surfaces to be joined, as well as removal of oxides from the solder, particularly when the solder is in a pre-form state. Solder bumps are a widely used type of pre-form solder, and are pervasively used in semiconductor manufacturing bonding operations, e.g., for chip-to-chip and chip-to-package interconnect structures. Although fluxless methods of joining components have been developed, fluxes continue to be widely used, due in no small part to their ability to function as a temporary adhesive to fix a chip in place prior to the reflow (solder bonding) process.
Numerous varieties of fluxes are in common use. Many of such fluxes are rosin-based, and many fluxes contain halogens, e.g., chlorine. When these type of fluxes are employed, residual flux must be removed after joining, in order to prevent corrosion resulting from the oxidation-promoting component(s) of the flux composition, as well as to allow effective encapsulation to be performed, when encapsulation is carried out in connection with the joining process.
As integrated circuitry continues to densify, the use of flip-chip solder bonding has increased. In flip-chip bonding, the use of the flip-chip flux as a temporary adhesive is important in preserving alignment of the chip interconnect with the package pads between the placement and reflow steps.
A significant problem with flip-chip bonding is the need to remove all residual flux from the space between the chip and the package, with the difficulty being attributable to the relatively narrow separation of the chip and package, as well as the proximity of the solder balls to each other (in the array of solder bumps that is typically employed for the bonding operation). This proximity prevents good circulation and removal of conventional cleaning media, such as polar organic solvents, used for removing the residual flux.
As another cleaning operation commonly employed in semiconductor processing, chemical reservoirs are conventionally cleaned between successive charges. Chemical reservoirs are utilized in a variety of unit operations in the manufacture of microelectronic devices and thin film structures. Such chemical reservoirs must be completely cleaned and dried prior to each use, in order to maintain the high-purity character of the reagent that is held in and dispensed from the reservoir in subsequent operation. Conventional reservoir cleaning processes employed in the industry frequently include the following steps: (1) rinsing of the chamber with copious amounts of organic solvents to solubilize and remove residual chemical remaining from prior precursor charging of the reservoir, (2) washing of the reservoir with acids to remove acid-reactive residues and produce an uncontaminated reservoir surface for holding chemical in subsequent active operations, (3) thorough rinsing with copious amounts of de-ionized water to remove the acids and other residues in the reservoir, (4) rinsing of the reservoir with dry (anhydrous) organic solvents, e.g., isopropanol, acetone, and the like, to remove any residue not removed in the prior water rinsing step, and (5) drying of the reservoir.
Such cleaning processes employ large amounts of organic solvents, producing substantial volumes of organic waste and increasing the cost of the process, due to the necessity of solvent abatement and reclamation operations, to comply with applicable environmental and safety regulations. These conventional cleaning processes also have an associated deficiency when aqueous rinsing is employed, since any adsorbed water can be difficult to remove from the reservoir. If remaining in the reservoir as a residue, such adsorbed water can cause degradation of chemical reagents, when the reservoir is refilled with the chemical reagent and returned to active processing service. The degradation of the chemical reagent in turn may result in the manufactured semiconductor product being deficient or even useless for its intended purpose.
The above-discussed problems incident to conventional flux cleaning and reservoir cleaning operations are also present in various respects in the cleaning of microelectronic substrates and device thin film structures, as conventionally carried out to remove residues and extraneous material from the microelectronic device or precursor structure during its fabrication. Currently, many integrated circuitry manufacturing processes require aqueous-based cleaning, e.g., for removal of lithographic resist residues after etch removal of the resist. Although these cleaning processes are extremely well-developed and widely implemented in semiconductor manufacturing operations, such processes are substantially less useful and effective in application to high-aspect ratio vias and other finely-dimensioned features. This deficiency is due primarily to the high surface tension of aqueous solutions used for cleaning of structures having critical dimensions less than 0.1 micron. In such application, capillarity and wetting characteristics of the aqueous cleaning composition prevent penetration of the sub-micron structures, with the result that contaminants and extraneous materials are not removed from the finely-dimensioned features of the microelectronic device.
Further, in application to cleaning of low dielectric constant materials such as copper-porous low k multi-layer structures, special non-aqueous processing may be required to eliminate moisture uptake of porous low k dielectrics from the aqueous cleaning composition, in order to maintain suitable k values. Additionally, the dielectric constant of low k materials is critical and aqueous contamination can negatively increase dielectric constants and reliability of such materials.
For all of the foregoing reasons, the semiconductor manufacturing industry is in continuing need of improved cleaning reagents and methods to overcome the above-discussed problems associated with conventional cleaning techniques and materials.